270 ENVIRONMENTALENGINEERING
as a raw material. The tar contains water that must be removed; the charcoal is full of
glass and metal that must be separated. These separations render the by-products too
expensive to be competitive. Pyrolysis reduces the volume considerably, produces a
stable end product, and has few air pollution problems. On a large scale, such as for
some of our larger cities, pyrolysis as a method of volume reduction has significant
advantages over incineration. Pyrolysis may also be used for sludge disposal, thus
solving two major solid waste problems for a community. Such systems, however,
remain to be proven in full-scale operation.
Another method of volume reduction is baling. Solid waste is compressed into
desk-sized blocks that can then be handled with fork lifts and stacked in the landfill
depression. Because of the high density of the refuse (on the order of 2000 lb/yd3),
the rate of decomposition is slow and odor is reduced. Baled refuse does not therefore
require daily cover, further saving landfill space. Local and state regulations may,
however, require baled refuse landfills to provide daily cover, which substantially
reduces the cost advantages of baling.
CONCLUSION
This chapter begins by defining the objective of solid waste disposal as the placement
of solid waste so that it no longer impacts society or the environment. At one time, this
was fairly easy to achieve: dumping solid waste over city walls was quite adequate.
In modern civilization, however, this is no longer possible, and adequate disposal is
becoming increasingly difficult.
The disposal methods discussed in this chapter are only partial solutions to
the solid waste problem. Another solution would be to redefine solid waste as a
resource and use it to produce usable goods. This idea is explored in the next
chapter.
PROBLEMS13.1 Suppose that the municipal garbage collectors in a town of 10,000 go on
strike, and as a gesture to the community, your college or university decides to
accept all city refuse temporarily and pile it on the football field. If all the people
dumped refuse into the stadium, how many days must the strike continue before
the stadium is filled to 1 yard deep? Assume the density of the refuse as 300
lb/yd3, and assume the dimensions of the stadium as 120 yards long and 100 yards
wide.
13.2 If a town has a population of 100,000, what is the daily production of
wastepaper?
13.3 What would be some environmental impacts and effects of depositing dewa-
tered (but sloppy wet) sludge from a wastewater treatment plant into a sanitary
landfill?